Time and Work Questions

FACTS  AND  FORMULAE  FOR  TIME  AND  WORK  QUESTIONS

 

 

1. If A can do a piece of work in n days, then A's 1 day's work =1n

2. If A’s 1 day's work =1n, then A can finish the work in n days.

 

3. A is thrice as good a workman as B, then:

Ratio of work done by A and B = 3 : 1.

Ratio of times taken by A and B to finish a work = 1 : 3.

 

NOTE : 

Efficiency1No of time units

 

 Efficiency × Time = Constant Work

 

Hence, Required time = WorkEfficiency

 

Whole work is always considered as 1, in terms of fraction and 100% , in terms of percentage.

In general, number of day's or hours = 100Efficiency

Q:

A town having teenagers(boys & girls) of 5000 requires 150 litre of water per head. It has a tank measuring 20 m × 15 m × 5 m. The water of this tank will sufficient for ____ days.

A) 8 B) 6
C) 4 D) 2
 
Answer & Explanation Answer: D) 2

Explanation:

Total Water reqduired = 5000 × 150 lit = 750,000 litres = 750 cu.m.

 

Volume of tank = 20 × 15 × 5 = 1500 Cu.m.

 

Number of days required =1500/750 = 2 days.

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6 2815
Q:

A, B and C together can finish a task in 12 days. A is twice as productive as B and C alone can do the task in 36 days. In how many days can A and B do the task if C goes on leave?

A) 10 B) 20
C) 15 D) 18
 
Answer & Explanation Answer: D) 18

Explanation:
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Q:

12 men complete a work in 14 days. 5 days after they had started working, 3 men join them. How many more days will all of them take to complete the remaining work?

A) 5 B) 4
C) 3 D) 2
 
Answer & Explanation Answer: C) 3

Explanation:

Let p be the required number of days.

From the given data,

12 x 14 = 12 x 5 + (12+3) x p 

12 x 14 = 12[5 + 3p]

14 = 5 + 3p

3p = 9

p = 3 days.

 

Hence, more 3 days all of them take to complete the remaining work.

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Q:

A shopkeeper has a job to print certain number of documents and there are three machines P, Q and R for this job. P can complete the job in 3 days, Q can complete the job in 4 days and R can complete the job in 6 days. How many days the shopkeeper will it take to complete the job if all the machines are used simultaneously ?

A) 4/3 days B) 2 days
C) 3/2 days D) 4 days
 
Answer & Explanation Answer: A) 4/3 days

Explanation:

Let the total number of documents to be printed be 12.

 The number of documents printed by P in 1 day = 4.

 The number of documents printed by Q in 1 day = 3.

 The number of documents printed by R in 1 day = 2.

 
Thus, the total number of documents that can be printed by all the machines working simultaneously in a single day = 9.

 

Therefore, the number of days taken to complete the whole work = 12/9 = 4/3 days.

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Q:

Three athletes can complete one round around a circular field in 16, 24 and 36 min respectively. They start running together at same instant then after how much time they will meet to each other for first time ?

A) 2 hrs 24 min B) 2 hrs 44 min
C) 1 hrs 24 min D) 1 hrs 24 min
 
Answer & Explanation Answer: A) 2 hrs 24 min

Explanation:

Given that three athletes can complete one round around a circular field in 16, 24 and 36 min respectively.

Now, required time after which they met for the first time = LCM of (16, 24 & 36) min

Now, LCM of 16, 24, 36 = 144 minutes = 2 hrs 24 min.

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14 2633
Q:

A alone can do a work in 20 days. B is 125% more efficient than A. A and B started working and worked for 4 days. If C alone completed the remaining job in 22 days. How many days C alone takes to complete the entire job?

A) 30 B) 35
C) 40 D) 42
 
Answer & Explanation Answer: C) 40

Explanation:
A alone can do = 20days 
 
Efficiency ratio of A & B= 4 : 5

Time required will be in ratio = 5:4

B alone will do it in =16 days

LCM of (16,20)= 80 ,
 
Assume work size of 80 units

 

1 day work of A= 4 units 1 day work of B= 5 units

 

Work done by both in 4 days= 4*(5+4)= 36 units

 

Work left= 80-36= 44 units

 

Now C takes 22 days to complete= 44 units.

 

Time taken by C alone to complete the work= 40 days
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Q:

5 boys and 3 girls can together cultivate a 23 acre field in 4 days and 3 boys and 2 girls together can cultivate a 7 acre field in 2 days. How many girls will be needed together with 7 boys, if they cultivate 45 acres of field in 6 days?

A) 4 B) 3
C) 2 D) 1
 
Answer & Explanation Answer: C) 2

Explanation:

Let workdone 1 boy in 1 day be b

and that of 1 girl be g

From the given data,

4(5b + 3g) = 23

20b + 12g = 23 .......(a)

 

2(3b + 2g) = 7

6b + 4g = 7 ........(b)

 

Solving (a) & (b), we get

b = 1, g = 1/4

 

Let number og girls required be 'p'

6(7 x 1 + p x 1/4) = 45

=> p = 2.

 

Hence, number of girls required = 2

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Q:

Tushar takes 6 hours to complete a piece of work, while Amar completes the same work in 10 hours. If both of them work together, then what is the time required to complete the work?

 

A)  3 hours B) 3 hours 15 minutes
C) 3 hours 30 minutes D) 3 hours 45 minutes
 
Answer & Explanation Answer: D) 3 hours 45 minutes

Explanation:

Let them take x hours working together

1/x = 1/10 + 1/6 = 8/30

X= 30/8 hours = 15/4 hours = 3 hours 45 minutes

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